The GameLine was a cartridge for the Atari 2600 which could download games using a telephone line. It was a third party accessory made by Control Video Corporation (CVC), who also ran the GameLine service.
In the early 1980s a cable pioneer named William von Meister was looking for a way to use his innovative modem transmission technology, which previously was acquired in ill-fated attempts of sending music to cable companies. Legal issues caused cable providers to step away from the service, leaving Von Meister with a delivery tool and no content.
He then converted his variable speed adaptive modem technology to download games from central servers to individual households. This allowed users to call up a system and, for a fee, download games to their GameLine modules. The game would typically work for 5-10 plays, after which the user would have to connect to GameLine again and pay for another download.
Physically, the Master Module, as it was called, looked like an oversized silver Atari cartridge, it had a phone jack on the side that was used to link the Master Module with the CVC computers. The module was able to transmit with pulse or tone dialing, allowing the unit to be versatile in the field. The games available on the GameLine service were all from third-party gamemakers, the largest of which was Imagic (whose catalog is now controlled by Activision). CVC tried, but failed to obtain licensing agreements from the largest game makers, such as Atari, Activision, Coleco, Mattel, and Parker Brothers.